The present invention relates to photochemical sensors and methods for the production thereof.
More particularly, the present invention relates to an indicator dye nanoporous photochemical sensor composite glass films and processes for the preparation thereof, as well as to the use thereof in the preparation of a fiber optic and/or wave-guiding photochemical sensor for detecting environmental impurities.
The present invention enables the preparation of stable, multi-use remote sensors for detection systems for environmental impurities which allow monitoring in situ of traces of impurities such as ammonia, acid rain and bases in the atmosphere, the water and the ground, and chlorinated hydrocarbons in ground waters and soils, based on the introduction of indicator dyes into a novel composite glass film from which sensitive waveguides are fabricated.
The concept of applying optical guides and fiber optical sensors to the detection of various environmental impurities is not new, and has been pursued for over a decade. (See, e.g., W. R. Seitz, xe2x80x9cChemical Sensors Based on fiber Optics,xe2x80x9d Anal. Chem., Vol. 56, p. 16A (1984); D. W. Luebbers and N. Opitz, xe2x80x9cOptical Fluorescence Sensors for Continuous Measurements of Chemical Concentration in Biological Systems,xe2x80x9d Sensors Actuators, Vol. 4, p. 641 (1983); and E. J. Poziomek, xe2x80x9cFiber Optic Sensors, A Review,xe2x80x9d Proc. of the Third Biennial Dept. of Defense Fiber Optics Conference, pp. 115-119, McLean, Va., U.S.A. (March 1992).)
The use of optical fibers for remote spectroscopy predates the use of fibers in communication systems, and continues to be an important technique in environmental, biomedical and process-control sensing. Recent progress in fiber optic chemical sensing, including the development of optically active sensors, intrinsically sensitive fibers, new sensor chemistries, and sensors based on integrated optic devices, has greatly expanded the range of application of chemical and environmental fiber optic sensors.
Two main configurations can be considered, using either the end fiber or the evanescent wave technique. In the first case, a dye-doped material (polymer or porous glass) is attached to the end of an optical fiber which is only used to relay the sensitive dye fluorescence (or absorption) signal. In the second case, the fiber itself becomes part of the sensing element, which consists of a dye-doped cladding coated onto the fiber core. The evanescent field of a guided radiation can excite the dye, which interacts selectively with the analyte and modulates the light signal. This approach offers a shorter response time and a distributed sensing; a spatial profile of the analyte concentration is provided along the length of the fiber.
Though it may not be apparent in first examination of current work on development of fiber optic sensors for hazardous materials, much of this research involves immobilization of the indicator molecules. Examples of substrates examined recently include porous glass and porous polymers (see, e.g., M. Bocci, F. Baldwin and S. Bracci, xe2x80x9cSpectroscopic Behavior of Acid-Base Indicators after Immobilization on Glass Supports,xe2x80x9d Appl. Spectrosc., Vol. 45, No. 9, pp. 1508-1515 (1991); and M. B. Tabacco, Q. Zhou, K. Rosenblum and M. R. Shahriari, xe2x80x9cChemical Sensors for Hazardous Waste Monitoring,xe2x80x9d Proc. of the Second International Symposium on Field-Screening Methods for Hazardous Wastes and Toxic Chemicals, U.S. Environmental Protection Agency, Las Vegas, Nev., U.S.A. (February 1991)); M. Bocci, F. Baldinin and S. Bracci, xe2x80x9cSpectroscopic Behavior of Acid-Base Indicators after Immobilization on Glass Supports,xe2x80x9d Appl. Spectrosc., Vol. 45, No. 9, pp. 1508-1515 (1991); and C. Rottman, M. Ottolengi, R. Zusman, et al., xe2x80x9cDoped Sol-Gel Glasses as pH Sensors,xe2x80x9d Matt. Lett., Vol. 13, pp. 293-298 (1992)); linear-chain, rigid-rod polymers (W. P. Carey and B. S. Jorgensen, xe2x80x9cOptical Sensors for High Acidities Based on Fluorescent Polymers,xe2x80x9d Appl. Spectrosc., Vol. 45, No. 5, pp. 834-838 (1991)); polybenzimidazol and FormvarR (L. C. Baylor and P. E. O""Rourke, xe2x80x9cFiber Optic pH Sensors,xe2x80x9d NUCL 89, Abstracts of Papers, 201st American Chemical Society National Meeting, Atlanta, Ga., U.S.A. (April 1991)); cellulose acetate (T. P. Jones, S. J. Coldron, W. J. Deninger and M. D. Porter, xe2x80x9cA Field-Deployable Dual Wavelength Fiber Optic pH Sensor Instrument Based on Solid-State Optical and Electrical Components,xe2x80x9d App. Spectrosc., Vol. 45, No. 8, pp. 1271-1276 (1991)); quartz powder (M. F. McCurley and W. R. Seitz, xe2x80x9cFiber Optic Chemical Sensors Based on Polymer Swelling,xe2x80x9d ANYL 61, Abstracts of Papers, 201st American Chemical Society National Meeting, Atlanta, Ga., U.S.A. (April 1991)); poly(vinyl alcohol) with oxiran group (J. Reichert, R. Czolk, W. Sellien and A. J. Ache, xe2x80x9cChemical Sensors in Environmental Analysis: Ammonium and Cadmium Sensors,xe2x80x9d NATO ASSI Ser., Ser G 1991, pp. 195-211 (Chem. Abstr. 115:84318p)); dimethyl silicone powder (S. M. Barnard and D. R. Walt, xe2x80x9cFiber Optic Organic Vapor Sensor,xe2x80x9d Environ. Sci. Techn., Vol. 25, No. 7, pp. 1301-1304 (1991)); and cellulose triacetate (C. Jian and W. R. Seitz, xe2x80x9cMembrane for In Situ Optical Detection of Organic Nitro Compounds Based on Fluorescence Quenching,xe2x80x9d Anal. Chim. Acta, Vol. 237, No. 2, pp. 265-271 (1991)).
Ethyl cellulose has been proposed as a coating standard for mass sensors, but could be used as a xe2x80x9cstandardxe2x80x9d substrate for fiber optic sensors as well (see, e.g., E. J. Poziomek, J. Li, H. Wohitjen and N. L. Jarvis, xe2x80x9cEthyl Cellulose as a Coating Standard for Mass Sensors,xe2x80x9d Third International Symposium on Field Screening Methods for Hazardous Wastes and Toxic Chemicals, Las Vegas, Nev., U.S.A. (February 1993)).
However, design of immobilized indicator materials, and meeting needs of sensitivity and selectivity are not trivial, as pointed out and explained by E. J. Poziomek, xe2x80x9cTechnology Barriers in the Development of Fiber Optic and Other Chemical Sensors for Field Screening,xe2x80x9d Oak Ridge National Laboratory Life Sciences Symposium, Gatlinburg, Tenn., U.S.A. (May 1990), published in Hazardous Waste Site Investigation, R. B. Gammage and B. A. Berven, Eds., Lewis Publishers, Ann Arbor, Mich., U.S.A. (1992).
Furthermore, there is a severe drawback in incorporating the organic indicator dyes into the traditional host matrices. Depending on the nature of the polymer, the sensor probe is not necessarily inert with respect to the dye, as free radicals tend to be formed under photo-excitation. These radicals tend to strongly reduce the absorption and luminescence characteristics of the dyes. The polymeric matrices may also provide a reductive atmosphere, which will react with the photo-excited states of the dyes and will change their chemical constitution with time. It is therefore of vital interest to develop inert, highly transparent host matrices which are stable and which can be used for remote sensors for environmental and biological impurities.
Purely inorganic matrices, on the other hand, furnish too polar environment for entrapped organic indicator molecules, which may cause them to agglomerate at high concentrations and thus prevent high sensitivity.
In 1990, the present inventor and others published an article, entitled xe2x80x9cOxazine-170 in Sol-Gel Glass and PMMA Films as a Reversible Optical Waveguide Sensor for Ammonia and Acids,xe2x80x9d (V. Chernyak, R. Reisfeld, R. Gvishi and D. Venezky, Sensors and Materials, Vol. 2, No. 2 pp. 117-126 (1990)). In this article, there were described sensors for ammonia and acids based on Oxazine-170 dye, incorporated into sol-gel glasses prepared from tetraethoxysilane. However, the kinetics of the ammonia diffusion was too slow to be used for practical purposes, if the films were not thin enough. On the other hand, Oxazine-170, incorporated into polymethylmethacrylate (PMMA) gave a very good response; however, the sensor was not stable enough and deteriorated quickly.
Earlier in 1993, the present inventor published a further article, entitled xe2x80x9cPhotochemical SeBased on Malachite Green in Glass Films,xe2x80x9d (V. Chernyak and R. Reisfeld, Sensors and Materials, Vol. 4, No. 4, pp. 195-204 (1993)). As described and explained therein, glass films containing malachite green are sensitive glass waveguide sensors (optrodes) for acid and ammonia vapor or solutions. The different color changes are the result of the yellow H(MG)2+ dication, blue-green monocation (MG)+ and colorless carbinol base HO(MG), and depend on the pH of the. surroundings. The method enables the preparation of optically active waveguides with the sensitivity of 1-2 ppm for ammonia. These sensors are all solid state, based on organic indicators incorporated in sol-gel matrices. The concept of applying optical guides and fiber optical sensors for detection of various environmental impurities has been suggested recently (J. Janata and A. Bezegh, Anal. Chem., Vol. 60, p. 62R (1988 and 1990)).
In 1996 present inventors published an article xe2x80x9cReversible Optical Sensor for In Situ Determination of Heavy Metal Impurities in the Environmentxe2x80x9d. (D. Shamrakov and R. Reisfeld, Sensors and Materials, 8, (1996) 439-443). A technique was suggested for generation of nanoporous sol-gel silica coatings with fluorescent indicator entrapped in it. An optimal structure was achieved, where on one hand the pores were wide enough to provide fast migration of the analyte ions to the indicator molecules inside the glass, but small enough, on the other hand, to prevent the dye leaching and thus sensor deterioration. Reversible operation of sensor for cadmium was demonstrated, which was not however free of disadvantages of an inorganic matrices mentioned above.
In principle, such a system may be composed of a small light source, for example, a light-emitting diode (LED) coupled with a capillary tube covered by a reagent which, by reacting with the impurities, changes its color. The activated tube may be coupled to a filter and photodetector, which appropriately measures either transmission of light or emission induced by the light of the reaction product. In this way it is possible to detect and quantitatively measure traces of ammonia, acids (acid rain) and biological impurities.
While it was found that malachite green was indeed a useful indicator dye in such a system, the sol-gel matrix employed was still unsatisfactory.
With the above-described state of the art in mind, according to the present invention there is now provided an indicator dye nanoporous photochemical sensor composite glass film, comprising a multiplicity of polyacrylate chains intertwined with a multiplicity of cross-linked networks of silica and doped with an indicator dye, wherein said film is formed with a plurality of nanopores sized in the range between 20 and 200 angstrom for the entry of analytes to be detected thereby
In another aspect of the present invention, there is now provided a process for the preparation of an indicator dye nanoporous photochemical sensor composite glass, comprising a multiplicity of polyacrylate chains intertwined with a multiplicity of cross-linked networks of silica and doped with an indicator dye, said process comprising the steps of:
a) forming a solution of at least one alkoxysilane precursor, water, ethanol and a catalyst to effect the hydrolysis of said precursor;
b) adding a solvent selected from the group consisting of benzene and toluene;
c) effecting azeotropic distillation of the resulting solution to remove water and alcohol;
d) adding glacial acetic acid and distilling off said original solvent while adding an indicator dye, whereby said benzene or toluene are replaced with glacial acetic acid and any water entrained in said dye is removed by said distillation;
e) introducing a polyacrylate of the general formula I: 
xe2x80x83wherein:
R is hydrogen, methyl or ethyl;
R1 is hydrogen, methyl or ethyl, and
n is a whole integer greater than 100
into the remaining solution; and
f) distilling off said glacial acetic acid,
whereby there is formed a silica-polymer composite glass solution doped with an indicator dye;
g) applying a coating of said solution on a suitable substrate; and
h) evaporation of the solvent under elevated temperature in a closed chamber.
Preferably, in the above formula, n is between 100 and 1,000, R can have different values in the same polymer, and R1 can also have different values in the same polymer.
The invention also provides a wave-guiding sensor comprising a silica-polymer composite glass film doped with an indicator dye, as described herein.
In the above process, it is preferred that the said alkoxysilane precursors have one to four carbon atoms in each of said alkoxy groups; tetraalkoxysilanes, such as tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane and tetrabutoxysilane are preferred.
In an especially preferred embodiment of the present invention, said precursors are tetraalkoxysilane intermixed with a trialkoxysilane derivative having a C2-C6 unsaturated aliphatic chain with one or two double bonds.
Preferred polyacrylates for use in the present invention are polymethylmethacrylate, polyethylmethacrylate, polyacrylic acid and polymethacrylic acid.
In U.S. Pat. No. 5,783,319 by two of the present inventors, there is described and claimed waveguide tunable lasers and processes for the production thereof, wherein a composite glass film waveguide tunable laser is described and claimed. While said lasers are similar to those of the present invention, they are different in structure in that they are continuous and non-porous and therefore cannot be used as photochemical sensors, since analytes cannot enter the film described and formed by the process of said patent. Therefore, said patent neither teaches nor suggests the sensors of the present invention, nor the methods for the production thereof.
The invention will now be described in connection with certain preferred embodiments with reference to the following illustrative figures so that it may be more fully understood.
With specific reference now to the figures in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the preferred embodiments of the present invention only, and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice.